Q.Integrate the function tan−11+x1−x
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Integration by Parts
The idea: reverse the product rule
Some integrands are a product of two very different functions — xex, xcosx, logx, xsin−1x — where substitution gets you nowhere. Integration by parts is the tool for these. It comes straight from reversing the product rule for differentiation.
Starting from dxd(uv)=uv′+u′v and integrating both sides gives the working formula:
∫udxdvdx=uv−∫vdxdudx.
In words: integral of (first × derivative-of-second) = first × integral-of-second − integral of (derivative-of-first × integral-of-second).
Choosing u: the ILATE rule
The whole game is picking which factor is u (to differentiate) and which is dv (to integrate). Pick u by ILATE — the first type that appears:
- Inverse trig (sin−1x), Logarithmic (logx), Algebraic (x2), Trigonometric (sinx), Exponential (ex).
Whatever comes first in ILATE becomes u; the rest is dv. This makes the new integral ∫vdu simpler than the one you started with.
Worked idea
For ∫xexdx: algebraic before exponential, so u=x, dv=exdx. Then du=dx, v=ex:
∫xexdx=xex−∫exdx=xex−ex+C=ex(x−1)+C. …
Concept: Power Rule Integration — after a trigonometric substitution, the integrand simplifies to a standard form.
Let x=cos2θ, so 1+x1−x=1+cos2θ1−cos2θ=2cos2θ2sin2θ=tanθ.
Then tan−1(tanθ)=θ (for principal values), and dx=−2sin2θdθ.
The integral becomes:
∫θ⋅(−2sin2θ)dθ=−2∫θsin2θdθ
Integrate by parts: let u=θ, dv=sin2θdθ, so du=dθ, v=−21cos2θ.
Then: …
The substitution x=cos2θ turns the integrand into the simple angle θ=21cos−1x. Integrating by parts and returning to x gives xtan−11+x1−x−211−x2+C.
The key simplification
Let x=cos2θ. Then
1+x1−x=1+cos2θ1−cos2θ=2cos2θ2sin2θ=tan2θ,
so 1+x1−x=tanθ and the integrand becomes tan−1(tanθ)=θ (for θ∈[0,2π)). Since θ=21cos−1x, the integral reduces to 21∫cos−1xdx.
Step-by-step solution
1. Reduce the integral.
I=∫tan−11+x1−xdx=21∫cos−1xdx.
2. Integrate by parts with u=cos−1x, dv=dx:
∫cos−1xdx=xcos−1x−∫x⋅1−x2−1dx=xcos−1x+∫1−x2xdx=xcos−1x−1−x2.
3. Combine. …
Method: Trig substitution to simplify an inverse-trig integrand, then integrate by parts
Use this when the integrand is an inverse trig function of a surd like tan−11+x1−x: a substitution such as x=cos2θ turns the whole thing into a simple angle.
Steps
Step 1: Substitute to unwrap the inverse trig.
Put x=cos2θ. Then 1+x1−x=tan2θ, so 1+x1−x=tanθ and tan−1(tanθ)=θ=21cos−1x. …
Common Mistakes
Mistake 1: Trying to integrate tan−11+x1−x directly.
Why it's wrong: the nested surd inside an inverse-trig has no direct antiderivative; a substitution is needed first. Correct approach: put x=cos2θ to reduce it to 21cos−1x.
Mistake 2: Wrong half-angle reduction.
Why it's wrong: 1+cos2θ1−cos2θ=tan2θ; a slip here breaks the simplification. Correct approach: use 1−cos2θ=2sin2θ, 1+cos2θ=2cos2θ. …
Showing the 12 most recent of 40 on this concept.
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Put t=x; the integral becomes 2∫tcostdt=2(tsint+cost)+k.
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- CBSE 2026Set A1 markMCQQ.∫ex(tan−1x+1+x21)dx=(a) extan−1x+k(b) ex⋅1+x21+k(c) ex+k(d) tan−1x+k
›Reveal solutionSolution
Recognise ∫ex[f(x)+f′(x)]dx=exf(x)+k; here f(x)=tan−1x.
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By parts: ∫01xexdx=[(x−1)ex]01=1.
Take u=x, dv=exdx, so du=dx, v=ex:
∫xexdx=xex−∫exdx=xex−ex=(x−1)ex.
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- CBSE 2026Set ANNUAL1 markMCQQ.Write the value of ∫ex(sinx−cosx)dx.(a) −excosx+c(b) exsinx+c(c) −exsecx+c(d) excosecx+c
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Recognising the standard form ∫ex[f(x)+f′(x)]dx=exf(x)+c gives −excosx+c.
There is a standard integration result:
∫ex[f(x)+f′(x)]dx=exf(x)+c
Compare the integrand sinx−cosx with f(x)+f′(x). Try f(x)=−cosx; then f′(x)=sinx, so
f(x)+f′(x)=−cosx+sinx=sinx−cosx …
- CBSE 2026Set ANNUAL1 markMCQQ.∫ex(logsecx+tanx)dx=(a) ex+C(b) extanx+C(c) ex(logsecx)+C(d) None of these
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This is of the standard form ∫ex[f(x)+f′(x)]dx=exf(x)+C.
Let f(x)=logsecx. Then f′(x)=secxsecxtanx=tanx.
…
- CBSE 2025Set X11 markMCQQ.∫ex(sinx−cosx)dx is(a) −excosx(b) excosx(c) exsinx(d) exsin2x
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Integral of the form ∫ex(f+f′)dx=exf — correct option (a). …
- CBSE 2025Set ANNUAL1 markQ.Find ∫x⋅exdx.
›Reveal solutionSolution
Apply integration by parts with u=x, dv=exdx.
…
- CBSE 2025Set E1 markMCQQ.∫logx2dx=(a) x21+k(b) x2+k(c) xlogx−x+k(d) 2(xlogx−x)+k
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Bring down the power, then integrate logx by parts; result 2(xlogx−x)+k.
First logx2=2logx. Now integrate ∫logxdx by parts with u=logx, dv=dx: …
- CBSE 2025Set ANNUAL1 markQ.Evaluate ∫xsinxdx.
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Use integration by parts (ILATE): take u=x (algebraic) and dv=sinxdx.
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…
- CBSE 2025Set ANNUAL1 markQ.Evaluate : ∫xlog2xdx
›Reveal solutionSolution
Use integration by parts, taking the logarithm as the first function.
Let I=∫xlog2xdx. Apply ∫udv=uv−∫vdu with
u=log2x,dv=xdx.
Then
du=2x1⋅2dx=x1dx,v=2x2.
Therefore
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- CBSE 2025Set ANNUAL1 markMCQQ.∫exsecx(1+tanx)dx is equal to(a) excosx+c(b) exsecx+c(c) exsinx+c(d) extanx+c
›Reveal solutionSolution
Recognise the form ∫ex{f(x)+f′(x)}dx=exf(x)+c.
Expand the integrand:
exsecx(1+tanx)=ex(secx+secxtanx).
Let f(x)=secx. Then
f′(x)=secxtanx.
So the integrand is exactly ex{f(x)+f′(x)}, and by the standard result
∫ex{f(x)+f′(x)}dx=exf(x)+c=exsecx+c.
Verification (differentiate the answer): …
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